Restrict StrOpt to just a few allowed values

Allow the developers to specify allowed parameter with a list
of values. Throw a ValueError when the value specified in
the command line or config file is not in the list of allowed
values

Fixes LP# 1123043

DocImpact

Change-Id: I69f5610dd738f808c7f2734e8abead0e26f8dadf
Merge "Restrict StrOpt to just a few allowed values"