add yosemite to macOSXSeries
Prevent destroy-environment when desired.
Fixed error construction and format. Renamed vars for clarity and conformity.
Cleaned up error-related code based on review.
Made code readable
Environment variable manipulation is behind cmds for block/unblock operation.
Code readability improvement.
state: extracted environment setup ops

The code to generated DB operations for setting up the initial
environment have been extracted so that they can also be called from
elsewhere.
move juju.{State,Life} to multiwatcher.{State,Life} and add aliases in apiserver/params
tests pass
remove unused file
Mock command for tests.
More verbose command purpose for help.
Move backupsMetaC into backups.go.
Move state/backups.go to state/backups/storage.go.
Use the common implementation for getting a new State.
Add a note about dropping the corresponding function in state.
Use *state.State rather than the temp surrogate interfaces.
Fix a couple storage names.
Gut the backup plugin, but keep it around for backward-compatibility.