Restart collectd when importing/decrypting a pool.

Scenario:
Assumption: There are both encrypted and unencrypted pools
1. FreeNAS boots and automounts unencrypted pools
2. collectd starts to track free space on the pools
3. User unlocks the encrypted pols
Before fix: collectd doesn't track free space of the "new" pools
After fix: collectd correctly starts tracking free space of the unlocked pools