Update presto-admin not to remove local connector files on connector remove

[mattsfuller]

A proposal from Brian, though likely without ".properties":
Help:
presto-admin connector add [connector name | all | all-force]
presto-admin connector add
Missing parameter: must specify property file name or 'all' or 'all-force'
presto-admin connector add hive.properties
Copying hive.properties to all nodes
...
presto-admin connector add all
Preparing to copy all connector configurations to all nodes:
hive.properties
psql.properties
tpch.properties
Are you sure? (yes or no)
Presto-admin connector add all-force
Copying all connector property files to all nodes:
hive.properties
psql.properties
tpch.properties
...
If we were to make these changes, then it would be appropriate to not delete the local config file for "connector remove".

[mattsfuller]

Leaving out ".properties" is fine. Also, if the user does not specify a connector, or if they specify one that doesn't exist, we should list the available connectors as part of the error message.
presto-admin connector add
Missing parameter: must specify existing property file name or 'all' or 'all-force'.
Connector property files are stored in /etc/opt/prestoadmin/connectors/.
Available connectors are:
hive
psql
tpch
presto-admin connector add tpcf
Invalid connector name 'tpcf': must specify existing property file name or 'all' or 'all-force'.
Connector property files are stored in /etc/opt/prestoadmin/connectors/.
Available connectors are:
hive
psql
tpch