Test SSHD running as another user

[micheelengronne]

Is your feature request related to a problem? Please describe.
I would like to test a sshd running in a container with another user.

Running a sshd with another user in a container environment is more secure than root.

Describe the solution you'd like
The possibility to set the user that replace root in the tests.
Handle UsePrivilegeSeparation no and UsePam no as stated here https://serverfault.com/questions/344295/is-it-possible-to-run-sshd-as-a-normal-user

[micheelengronne]

#152