Allow time unit variables to be 0

plugins.checkFrequency can be disabled by setting the time to 0,
but this is not allowed in a time unit typed variable due to the
regex requiring the value to start with a digit in the range 1-9.
Permit 0 as a value.

Change-Id: I2deca08fe9b0ea93ef23f626fc44cffe98ad2d95
2 files changed