Increases Gripper reboot state transistion buffer

The electric gripper plugins report ready when a ready flag is
received from the grippers. This flag is currently returned in
advance of the gripper fully returning to the ready state on a
reboot. This fix increases the buffer timeout for calibrate
commands from 0.5 to 1.0 seconds.
Merge pull request #34 from RethinkRobotics/gripper_reboot_fix

Increases Gripper reboot state transistion buffer