ovs-vtep: Use shlex module to split args.

ovs-vtep: Use shlex module to split args.

string.split() function splits a quoted string if there is a whitespace
inside the quote.
ex: The following code snippet will output ['printing', '"No', 'Diagnostic"']
args = 'printing "No Diagnostic"'
print args.split()

The above is a problem if we run the following command through vtep_ctl().
vtep-ctl set tunnel $uuid bfd_status:diagnostic="No Diagnostic"

The workaround is to use the split() function from shlex module.

Signed-off-by: Gurucharan Shetty <gshetty@nicira.com>
Acked-by: Ariel Tubaltsev <atubaltsev@vmware.com>
Acked-by: Justin Pettit <jpettit@nicira.com>