Rename "wait_for" to "wait_until"

Refs kamaki/grnet#46
Implement wait_server_while and wait_server_until

Refs grnet/kamaki#46

Retain backwards compatibility by keeping the "wait_server" method.
Implement a new method "get_status" to retrieve current server status
as well as a progress percentile if available.
Adjust CLI wait methods to support "until"

Refs grnet/kamaki#46
Use "--while" and "--until" in "server wait"

Refs grnet/kamaki#46

To new arguments  are mutually exclussive.

The argument "--status STATUS" is kept for backwards compatibility
and it will be removed in a future version.