Changing singleton usage

Changing singleton usage

We won't be talking to any more than one temporal cluster at a
time, so it does not make sense to have clients cached by API
endpoint.  Instead the main() of any program wanting to use
temporal can just set the class level variable and then simply
instantiate the class anywhere it is needed and it will
manage the cached client without needing the temporal API URL

Change-Id: Ia22635dc454e8df14ca22bc1e095f625d7e7337b
Signed-off-by: Mark Beierl <mark.beierl@canonical.com>