firebase CLI database:remove command not working in background mode

### [REQUIRED] Environment info
8.5.0

**firebase-tools:**

**Platform:**
Mac osx 10.15.5

### [REQUIRED] Test case
Backgroud Mode :
`firebase database:remove /path/mylarge_node_to_delete -y > /dev/null 2>&1 &`
Foreground mode :
`firebase database:remove /path/mylarge_node_to_delete -y ` is working fine. Able to delete the node

### [REQUIRED] Steps to reproduce
`firebase database:remove /path/mylarge_node_to_delete -y > /dev/null 2>&1 &`

### [REQUIRED] Expected behavior

Should start deleting the firebase node in background.

### [REQUIRED] Actual behavior

Node is not getting deleted. Firebase logs stops as mentioned below.

```
Aru-MacBook-Pro:~ arun$ tail -f -200 firebase-debug.log
[debug] [2021-06-07T10:39:02.340Z] ----------------------------------------------------------------------
[debug] [2021-06-07T10:39:02.344Z] Command: /Users/arun/.nvm/versions/node/v14.4.0/bin/node /Users/arun/.nvm/versions/node/v14.4.0/bin/firebase database:remove /instances/testbox-2TTakIR/PRODUCT_VARIANTS -y
[debug] [2021-06-07T10:39:02.344Z] CLI Version: 8.5.0
[debug] [2021-06-07T10:39:02.344Z] Platform: darwin
[debug] [2021-06-07T10:39:02.344Z] Node Version: v14.4.0
[debug] [2021-06-07T10:39:02.346Z] Time: Mon Jun 07 2021 16:09:02 GMT+0530 (India Standard Time)
[debug] [2021-06-07T10:39:02.346Z] ----------------------------------------------------------------------
[debug] [2021-06-07T10:39:02.346Z]
[debug] [2021-06-07T10:39:02.359Z] > command requires scopes: ["email","openid","https://www.googleapis.com/auth/cloudplatformprojects.readonly","https://www.googleapis.com/auth/firebase","https://www.googleapis.com/auth/cloud-platform"]
[debug] [2021-06-07T10:39:02.360Z] > authorizing via signed-in user
[debug] [2021-06-07T10:39:02.362Z] [iam] checking project shalfiparks-apps-qa for permissions ["firebase.projects.get","firebasedatabase.instances.update"]
[debug] [2021-06-07T10:39:02.367Z] >>> HTTP REQUEST POST https://cloudresourcemanager.googleapis.com/v1/projects/shalfiparks-apps-qa:testIamPermissions
{"permissions":["firebase.projects.get","firebasedatabase.instances.update"]}
[debug] [2021-06-07T10:39:03.621Z] <<< HTTP RESPONSE 200 {"content-type":"application/json; charset=UTF-8","vary":"X-Origin, Referer, Origin,Accept-Encoding","date":"Mon, 07 Jun 2021 10:31:37 GMT","server":"ESF","cache-control":"private","x-xss-protection":"0","x-frame-options":"SAMEORIGIN","x-content-type-options":"nosniff","server-timing":"gfet4t7; dur=1154","alt-svc":"h3-29=\":443\"; ma=2592000,h3-T051=\":443\"; ma=2592000,h3-Q050=\":443\"; ma=2592000,h3-Q046=\":443\"; ma=2592000,h3-Q043=\":443\"; ma=2592000,quic=\":443\"; ma=2592000; v=\"46,43\"","accept-ranges":"none","transfer-encoding":"chunked"}
[debug] [2021-06-07T10:39:03.623Z] >>> HTTP REQUEST GET https://firebase.googleapis.com/v1beta1/projects/shalfiparks-apps-qa

[debug] [2021-06-07T10:39:04.056Z] <<< HTTP RESPONSE 200 {"content-type":"application/json; charset=UTF-8","vary":"X-Origin, Referer, Origin,Accept-Encoding","date":"Mon, 07 Jun 2021 10:31:37 GMT","server":"ESF","cache-control":"private","x-xss-protection":"0","x-frame-options":"SAMEORIGIN","x-content-type-options":"nosniff","alt-svc":"h3-29=\":443\"; ma=2592000,h3-T051=\":443\"; ma=2592000,h3-Q050=\":443\"; ma=2592000,h3-Q046=\":443\"; ma=2592000,h3-Q043=\":443\"; ma=2592000,quic=\":443\"; ma=2592000; v=\"46,43\"","accept-ranges":"none","transfer-encoding":"chunked"}
```