Fix pexpect prompt expectations

- The old regex was not recognizing the prompt "Password:", it was
requiring a space after the :

- Verified that the pexpect regex does NOT have to match the entire
line.  Removing the space from the regex will match outputs with
any characters after the :
Add test for pexpect prompt changes
Merge pull request #56 from box/fix_pexpect_expectation_correctly

The fixes the reverted set of pexpect changes