Plugin fails to authenticate SSH for `ansible-galaxy install`

[markocelan]

Plugin fails to git clone roles in requirements.yaml if those roles are not publicly accessible.

Plugin supports private-key parameter which creates /tmp/privateKey* file containing private key for SSH auth, however this parameter is only passed to ansible command.
Unfortunately ansible-galaxy is unaware of this private key and is unable to authenticate.

Expectation:
When plugin excepts private_key parameter I would expect it to use this key consistently across all commands within this plugin.