bash_completion appears to be already installed if PROFILE variable is set on a system PROFILE file

[tcladet]

Operating system and version:

CentOS 7.6.1811

How did you install nvm?

curl -o- https://raw.githubusercontent.com/nvm-sh/nvm/v0.38.0/install.sh | NVM_DIR=/opt/nvm PROFILE=/etc/bashrc bash

What happened?

The output shows => bash_completion source string already in /etc/bashrc where this statement is wrong. This message pops just because the system PROFILE file case is not handled properly.

  % Total    % Received % Xferd  Average Speed   Time    Time     Time  Current
                                 Dload  Upload   Total   Spent    Left  Speed
100 14926  100 14926    0     0  57412      0 --:--:-- --:--:-- --:--:-- 57629
=> Downloading nvm from git to '/opt/nvm'
=> Cloning into '/opt/nvm'...
remote: Enumerating objects: 347, done.
remote: Counting objects: 100% (347/347), done.
remote: Compressing objects: 100% (294/294), done.
remote: Total 347 (delta 38), reused 171 (delta 28), pack-reused 0
Receiving objects: 100% (347/347), 197.06 KiB | 3.86 MiB/s, done.
Resolving deltas: 100% (38/38), done.
* (HEAD detached at FETCH_HEAD)
  master
=> Compressing and cleaning up git repository

=> Appending nvm source string to /etc/bashrc
=> bash_completion source string already in /etc/bashrc
=> Close and reopen your terminal to start using nvm or run the following to use it now:

export NVM_DIR="/opt/nvm"
[ -s "$NVM_DIR/nvm.sh" ] && \. "$NVM_DIR/nvm.sh"  # This loads nvm

What did you expect to happen?

As the vision of nvm is focused "per-user only", the detection function (that decide if the file set in PROFILE variable is a bash or zsh profile file) should detect if the file provided is a user one. If it is a system one, the installation should stop, or a BIG WARNING should pe printed.

[ljharb]

nvm is per-user - it should never go in the system bashrc file.

[tcladet]

Title and description edited as concluded in Pull Request #2569