Fix the auto_reloader to work when the executable was launched with a module

[ashleysommer]

Fixes #1492
Implements a detection routine when determining arguments for launching the child application, it checks if the executable was launched as a module, rather than a script, and if so launch the same module with the -m commandline argument again.

This PR also includes a different auto_reloader script, which passes the current cwd to the subprocess.call() call.

This is a basic workaround to get bugs in the current auto_reloader fixed for the 2019.03 sanic release.
We do intend to replace this simple naive auto_reloader in the future to be more robust one, that will potentially be implemented as a plugin.

[ashleysommer]

Can anyone work out what is causing the failure in the py35-no-ext test in travis?
The failure is in logging tests and is not related to this PR.
It seems that for some reason in py35 with no uvloop, the asyncio module is emitting a message to the caplog causing the caplog contents check to fail its assertion.
EDIT: I ran it again, with no modifications, it passed this time.

[codecov]

Codecov Report

Merging #1501 into master will decrease coverage by 0.36%.
The diff coverage is 0%.

@@            Coverage Diff            @@
##           master   #1501      +/-   ##
=========================================
- Coverage   91.46%   91.1%   -0.37%     
=========================================
  Files          17      17              
  Lines        1735    1742       +7     
  Branches      331     333       +2     
=========================================
  Hits         1587    1587              
- Misses        123     130       +7     
  Partials       25      25

Impacted Files	Coverage Δ
sanic/reloader_helpers.py	14.73% <0%> (-1.18%)	⬇️

---

Continue to review full report at Codecov.

Legend - Click here to learn more
Δ = absolute <relative> (impact), ø = not affected, ? = missing data
Powered by Codecov. Last update 34fe26e...3c01a2d. Read the comment docs.

[ashleysommer]

Codecov Diff is negative because there are no tests that touch the auto_reloader. So any modifications to the auto_reloader that add additional lines will decrease codecov further.

[sjsadowski]

Added #1504 as a follow-up to this (hopefully for 19.6)