Adds env variable to slience slow cli warning
Adds env variable to slience slow cli warning

We have some tests that assert against exact cli output, but at times
they run past the slow cli warning threshold and fail because the output
no longer exactly matches.  In order to enable consitent test runs we
are introducing and evnironment variable
'BOSH_CLI_SILENCE_SLOW_LOAD_WARNING'. If set it will not produce the
warning.

[Finishes #92469114]
Signed-off-by: Tyler Schultz <6b7a73f4f7cffc2a148becd12890940350ddfa95@pivotal.io>

barthy1/bosh,barthy1/bosh,barthy1/bosh,barthy1/bosh