Python3: fix syntax issue in _encode_item()

In Python 3, this is not a valid syntax:

    def _encode_item((k, v)): ...

Pass a single parameter to the function, and start by unpacking.

Change-Id: I73743073113a4696b9adc79bdb646575794c1e2b
Remove httplib2 requirement

There are no imports from httplib2 and everything seems to be converted
over to using the requests library now, so remove the extraneous
dependency.

Change-Id: I6a2a9543ea8f5da29494e1dba7659ec02a43deea
Merge "Remove httplib2 requirement"
Suppress expected help messages caused by wrong CLI inputs

There are negative tests for the NSX gateway feature. This
patch introduces the ability to suppress the warning messages
caused by running commands with wrong parameters. This keeps
the console output clean of spurious errors.

Change-Id: Idc78442969b3e06ecef9999a7edfc6544ed3a376
Closes-bug: #1311348
enable sorting support for agent listing

Change-Id: Ic11d0f9a0a53d765f85f8ffe3f12d50455236394
Closes-Bug: #1313607
Merge "enable sorting support for agent listing"
Removed now unnecesary workaround for PyPy

Related-bug: #1290562

Change-Id: I3fbfdcecfa19593729b1cb14685201207abc64a6
Merge "Removed now unnecesary workaround for PyPy"
Add ability to update certain attributes in a subnet

In testing the ability to update allocation_pools, I found that it was
not possible to do it.  This commits adds the ability to update those
attributes which are allowed in a PUT operation.

Added --enable-dhcp to the list of options.  The reason for adding it
was so that the help message would clearly show that it can be used
with a subnet-update command.  Otherwise, the end user may be confused
thinking there is no way to use subnet-update to enable dhcp for a
subnet where it is disabled.

DocImpact

Closes-Bug: #1324189
Change-Id: I52d05ec2284b6910a33df4a5cb7dc3888737acb6
added new column binary to the listing of agents

Change-Id: I057185ef2b6e248271597e81a6bef44c2ad8d148
Closes-Bug: #1313702
Merge "Add ability to update certain attributes in a subnet"
Merge "added new column binary to the listing of agents"
Merge "Python3: fix syntax issue in _encode_item()"
removed usage of '... can be repeated.'

Thanks to Diane Fleming for the wording.

Change-Id: Ida509a838a76f7484b004d59b2866f4dbf2075b6