Indexer shuts down node if prune mode is disabled?

Indexer was still running, but full node was shutdown
```
2020-12-15T00:09:40.945Z WARN pruner indexer/indexer.go:306 unable to prune lbrycrdd {"prune height": 868152, "error": "invalid response: 500 Internal Server Error {\"result\":null,\"error\":{\"code\":-1,\"message\":\"Cannot prune blocks because node is not in prune mode.\"},\"id\":1}\n: error pruning blockchain"}
github.com/lbryio/rosetta-lbry/indexer.(*Indexer).Prune
/app/src/indexer/indexer.go:306
main.startOnlineDependencies.func3
/app/src/main.go:108
golang.org/x/sync/errgroup.(*Group).Go.func1
/go/pkg/mod/golang.org/x/sync@v0.0.0-20201020160332-67f06af15bc9/errgroup/errgroup.go:57
2020-12-15T00:09:57.558Z DEBUG lbrycrdd lbry/node.go:56 UpdateTip: new best=d66047065472d35f8cdf561b9b652c51d654f762a46fb06ec7828b521b1c4cf8 height=878723 version=0x20000000 log2_work=74.026143 txb=151 tx=26229131 date='2020-12-12T17:54:19Z' progress=0.182868 cache=956.5MiB(2445908txo) IBD
2020-12-15T00:10:13.007Z DEBUG lbrycrdd lbry/node.go:56 UpdateTip: new best=c700e808aa053f8b3254e20b859b80137164e4e4d3c81c8f1f34c9e3ba683422 height=878730 version=0x20000000 log2_work=74.026155 txb=167 tx=26230115 date='2020-12-12T18:04:45Z' progress=0.183342 cache=957.5MiB(2449716txo) IBD
2020-12-15T00:10:29.568Z DEBUG lbrycrdd lbry/node.go:56 UpdateTip: new best=7d764d3b11ecb9d62b745b1eb60d8ad57e327f00d07de4a0cba85a25f0e88547 height=878738 version=0x20000000 log2_work=74.026171 txb=11 tx=26231889 date='2020-12-12T18:24:08Z' progress=0.184238 cache=958.8MiB(2453162txo) IBD
2020-12-15T00:10:49.008Z DEBUG lbrycrdd lbry/node.go:56 UpdateTip: new best=99d6e11b5f4ebd6bb3a4c2211b36f82c93ff51979b2c2ba5c61d8c291c15a8bf height=878744 version=0x20000000 log2_work=74.026184 txb=728 tx=26234057 date='2020-12-12T18:46:58Z' progress=0.185305 cache=960.2MiB(2456898txo) IBD
2020-12-15T00:10:52.745Z DEBUG memory utils/utils.go:62 stats {"heap (MB)": 3010.34708404541, "max heap (MB)": 8235.030403137207, "stack (MB)": 1.375, "system (MB)": 12090.720947265625, "garbage collections": 245}
2020-12-15T00:10:57.140Z WARN pruner indexer/indexer.go:286 exiting pruner
github.com/lbryio/rosetta-lbry/indexer.(*Indexer).Prune
/app/src/indexer/indexer.go:286
main.startOnlineDependencies.func3
/app/src/main.go:108
golang.org/x/sync/errgroup.(*Group).Go.func1
/go/pkg/mod/golang.org/x/sync@v0.0.0-20201020160332-67f06af15bc9/errgroup/errgroup.go:57
2020-12-15T00:10:57.141Z WARN lbrycrdd lbry/node.go:98 sending interrupt to lbrycrdd
github.com/lbryio/rosetta-lbry/lbry.Startlbrycrdd.func3
/app/src/lbry/node.go:98
golang.org/x/sync/errgroup.(*Group).Go.func1
/go/pkg/mod/golang.org/x/sync@v0.0.0-20201020160332-67f06af15bc9/errgroup/errgroup.go:57
2020-12-15T00:10:57.194Z DEBUG lbrycrdd lbry/node.go:56 tor: Thread interrupt
2020-12-15T00:10:57.215Z DEBUG lbrycrdd lbry/node.go:56 addcon thread exit
2020-12-15T00:10:57.215Z DEBUG lbrycrdd lbry/node.go:56 torcontrol thread exit
2020-12-15T00:10:57.215Z DEBUG lbrycrdd lbry/node.go:56 opencon thread exit
2020-12-15T00:10:57.215Z DEBUG lbrycrdd lbry/node.go:56 net thread exit
2020-12-15T00:10:57.220Z DEBUG lbrycrdd lbry/node.go:56 Shutdown: In progress...
2020-12-15T00:10:58.229Z DEBUG lbrycrdd lbry/node.go:56 msghand thread exit
2020-12-15T00:10:58.248Z DEBUG lbrycrdd lbry/node.go:56 scheduler thread interrupt
2020-12-15T00:10:58.257Z DEBUG lbrycrdd lbry/node.go:56 Dumped mempool: 0.002057s to copy, 0.001324s to dump

```

Start by reading indexer/indexer.go around lines 286 and 306, then follow the errgroup path from main.go:108 and the shutdown handling in lbry/node.go:98. Reproduce with prune mode disabled and verify that an unavailable prune operation does not shut down the full node.

Written by the indexing model from the issue text.