fix: cli - secator u install hangs on sudo prompt

[ocervell]

Hangs on sudo prompt, prompt is not shown to user.
Two ways to fix:

• either require user to type password: hard to wait for a prompt with the current implementation so might need to pass it secator u install --password <password>
• change command fabric to something more involved like 'invoke':

from invoke.runners import Local
from invoke.context import Context
context = Context()
runner = Local(context)
runner.start(cmd) # will prompt user for password if sudo is required
while runner.process.stdout.readline():
  # same processing as normal

[ocervell]

Fixed by #213