Add an option to run rootwrap as a daemon

Benchmark for daemon mode is to be added in next commit.

Current results on my machine for 'ip a':
        method          :    min       avg       max       dev
                   ip a :   3.701ms   4.966ms  12.720ms   1.206ms
              sudo ip a :  11.531ms  13.538ms  19.685ms   1.525ms
sudo rootwrap conf ip a :  92.253ms 119.431ms 211.236ms  17.948ms
     daemon.run('ip a') :   6.718ms   9.914ms 189.873ms  18.201ms

Implements: blueprint rootwrap-daemon-mode
Change-Id: Iace26738f910a18a5d1d3479fad949027e5a3816
Add daemon mode to benchmark

Change-Id: I9dbd71abc9cb7cca75582910be0eeefc27a1a174
Merge "Add an option to run rootwrap as a daemon"
Merge "Add daemon mode to benchmark"
Updated from global requirements

Change-Id: I227e5611243ddcdcc779736c657fd7d6ac04dad7
warn against sorting requirements

Change-Id: I64ae9191863564e278a35d42ec9cd743a233028e
Addresses-Bug: #1365061
Fix the bug tracker URL in CONTRIBUTING.rst

Change-Id: I464e04ab5b3cfac7a3ddd2a1784b5471b1fca7e8
Add a short doc to README on how to use daemon mode

Change-Id: I0e4e2cc35a2cbdc355d432c40b87e4aacc96da84
Initial cut of documentation for oslo.rootwrap

Closes-Bug: #1364141
Change-Id: If20de8767ff36b0a64c3b39f346d54a1ad6ca08f
Clean up title on main doc page

Make the title on the main documentation page consistent with the other
projects.

Change-Id: I8f15bfa8ace018f6e82e61a33fdbe20c96d8b8b9
Merge "Fix the bug tracker URL in CONTRIBUTING.rst"
Merge "Add a short doc to README on how to use daemon mode"
Merge "Initial cut of documentation for oslo.rootwrap"
Merge "Clean up title on main doc page"
Updated from global requirements

Change-Id: Ib6ae25e8ff6d141420736e702901a18dbd7af711