Trouble when using a sysimage with PythonCall

I'm having trouble when building a sysimage with PythonCall-- or rather, I can built it OK, but then when I use it, like

```julia
julia --project=myproject --sysimage=mysysimage.so -e "using Pkg; Pkg.instantiate()"
```

I get
```julia
#29 92.79 fatal: error thrown and no exception handler available.
#29 92.79 InitError(mod=:C, error=ErrorException("no environment in the LOAD_PATH depends on CondaPkg"))
#29 92.84 error at ./error.jl:33
#29 92.84 _jl_invoke at /buildworker/worker/package_linux64/build/src/gf.c:2247 [inlined]
#29 92.84 jl_apply_generic at /buildworker/worker/package_linux64/build/src/gf.c:2429
#29 92.84 _resolve_top_env at /root/.julia/packages/CondaPkg/GoPlj/src/resolve.jl:16
#29 92.84 _jl_invoke at /buildworker/worker/package_linux64/build/src/gf.c:2247 [inlined]
#29 92.84 jl_apply_generic at /buildworker/worker/package_linux64/build/src/gf.c:2429
#29 92.84 #resolve#17 at /root/.julia/packages/CondaPkg/GoPlj/src/resolve.jl:222
#29 92.84 _jl_invoke at /buildworker/worker/package_linux64/build/src/gf.c:2247 [inlined]
#29 92.84 jl_apply_generic at /buildworker/worker/package_linux64/build/src/gf.c:2429
#29 92.84 resolve at /root/.julia/packages/CondaPkg/GoPlj/src/resolve.jl:209
#29 92.84 _jl_invoke at /buildworker/worker/package_linux64/build/src/gf.c:2247 [inlined]
#29 92.84 jl_apply_generic at /buildworker/worker/package_linux64/build/src/gf.c:2429
#29 92.84 envdir at /root/.julia/packages/CondaPkg/GoPlj/src/env.jl:66
#29 92.85 init_context at /root/.julia/packages/PythonCall/Z6DIG/src/cpython/context.jl:56
#29 92.86 __init__ at /root/.julia/packages/PythonCall/Z6DIG/src/cpython/CPython.jl:21
#29 92.87 jfptr___init___72494 at /deps.so (unknown line)
#29 92.87 _jl_invoke at /buildworker/worker/package_linux64/build/src/gf.c:2247 [inlined]
#29 92.87 jl_apply_generic at /buildworker/worker/package_linux64/build/src/gf.c:2429
#29 92.87 jl_apply at /buildworker/worker/package_linux64/build/src/julia.h:1788 [inlined]
#29 92.87 jl_module_run_initializer at /buildworker/worker/package_linux64/build/src/toplevel.c:73
#29 92.87 _finish_julia_init at /buildworker/worker/package_linux64/build/src/init.c:796
#29 92.87 julia_init at /buildworker/worker/package_linux64/build/src/init.c:730
#29 92.87 jl_repl_entrypoint at /buildworker/worker/package_linux64/build/src/jlapi.c:695
#29 92.87 main at /buildworker/worker/package_linux64/build/cli/loader_exe.c:42
#29 92.88 __libc_start_main at /lib/x86_64-linux-gnu/libc.so.6 (unknown line)
#29 92.88 _start at /usr/local/julia/bin/julia (unknown line)
#29 93.11 ERROR: Failed to precompile MyPackage [...redacted...]
#29 94.21 Stacktrace:
#29 94.21 [1] error(s::String)
#29 94.60 @ Base ./error.jl:33
#29 94.77 [2] compilecache(pkg::Base.PkgId, path::String, internal_stderr::IO, internal_stdout::IO, ignore_loaded_modules::Bool)
#29 94.77 @ Base ./loading.jl:1466
#29 94.77 [3] compilecache(pkg::Base.PkgId, path::String)
#29 94.78 @ Base ./loading.jl:1410
#29 94.78 [4] _require(pkg::Base.PkgId)
#29 94.78 @ Base ./loading.jl:1120
#29 94.78 [5] require(uuidkey::Base.PkgId)
#29 94.78 @ Base ./loading.jl:1013
#29 94.78 [6] require(into::Module, mod::Symbol)
#29 94.78 @ Base ./loading.jl:997
```

(please excuse the `#29 92.79` stuff, I'm in a dockerfile here).

I believe the issue is that PythonCall's `__init__` tries to resolve the CondaPkg environment, but when a module is in a sysimage, that `__init__` occurs at startup time (i.e. when julia itself is starting up), and at that point in the process the package environment isn't setup yet... or something like that.