Showing list of available policies in case of wrong policy name

[pshahzeb]

If the policy name while creating a volume is wrong, and if valid policies exist, show their names as available options along with the error message

[root@sc-rdops-vm17-dhcp-12-47:~] /usr/lib/vmware/vmdkops/bin/vmdkops_admin.py policy ls
Policy Name  Policy Content                                              Active
-----------  ----------------------------------------------------------  ------
poltest4     (("proportionalCapacity" i0)("hostFailuresToTolerate" i0))  Unused
poltest      (("proportionalCapacity" i0)("hostFailuresToTolerate" i0))  Unused
poltest2     (("proportionalCapacity" i0)("hostFailuresToTolerate" i0))  Unused

root@photon-xVmYMbyTn [ ~ ]# docker volume create --driver=vsphere --name test_vol -o size=100MB -o vsan-policy-name=i_dont_exist
Error response from daemon: create test_vol: VolumeDriver.Create: Policy i_dont_exist does not exist. Available policies are: ['poltest2', 'poltest', 'poltest4']

Fixes #421

[msterin]

Pending CI pass (known issue failure is OK)

[msterin]

I love the message Policy i_dont_exist does not exist 👍

[shuklanirdesh82]

LGTM!