Prevent multiple device connections

RM#8865
Merge pull request #205 from Cerberus98/master

Quieter unit tests
Merge pull request #206 from rackerlabs/rm_8865

Prevent multiple device connections
RM9078

Implements pessimistic connection pooling to attempt to mitigate a
transient error causing connections to report "MySQL has gone away" but
not correctly recycle. The listener itself is contained in a
configuration variable defaulting to False.