Refine exception to ValueError
Start a shell before an inception environment is created
Unify the ssh code path

for screen_output = True or False, always use Popen and raise
exceptions correctly.
Specify ssh user for all ssh commands
Simplify the test ssh command to true
gateway node is default to a m1.tiny flavor
Print the ip instead of the FloatingIP object
Merge pull request #16 from maoy/working

Cleanup ssh