Buffer stats in influxdb driver before writing to the Db. The buffering duration
is configurable via a flag and is set to 60 seconds by default.
The storage driver test code has been refactored a bit to help test the new buffering
feature and will be future proof.

Docker-DCO-1.1-Signed-off-by: Vishnu Kannan <vishnuk@google.com> (github: vishh)
Simplify lock handling in influxdb driver.
Docker-DCO-1.1-Signed-off-by: Vishnu Kannan <vishnuk@google.com> (github: vishh)
Fix storage driver buffer duration default value.
The cache will now hold atlest the minimum number of stats required by the UI and more
if the buffer duration is longer than the default.

Docker-DCO-1.1-Signed-off-by: Vishnu Kannan <vishnuk@google.com> (github: vishh)