Add argparse into requirements

Add argparse into requirements.txt and heat_cfntools.egg-info
requires.txt

Fixes bug #1220071

Change-Id: I6147a8f14ac110d8dcdc1643ced5d32594322041
Change cfn-signal option --exit to --exit-code

According cfn user guide, the long option of cfn-signal -e should be
--exit-code.

Fixes bug #1220080

Change-Id: Id4e9feefd387a744f5e933aa4e9ea8a6f6f02a7c
Merge "Change cfn-signal option --exit to --exit-code"
Implement -k option for cfn-get-metadata

The -k argument can be a top-level key or a nested key in which case
the keys are separated by dots (eg "foo.bar"). In case a key contains a
dot character, it needs to be surrounded by single quotes (eg
"foo.'bar.1'.fred).
If the -k option is not provided, the command prints out the full
metadata structure as before.

Change-Id: Ib05d39672086001b83e8d7f56bc42cc4ba75751c
Fixes: bug #1183299