fix(cleaner): builder taking high CPU

[kmala]

Summary of Changes

This PR fixes the issue builder taking high CPU by waiting on the channel stream using select.

Issue(s) that this PR Closes

Fixes #280

Testing Instructions

After the fix:

CONTAINER           CPU %               MEM USAGE / LIMIT     MEM %               NET I/O             BLOCK I/O
5be5bad7ce1a        0.32%               22.45 MB / 3.892 GB   0.58%               0 B / 0 B           0 B / 0 B

Testing:

1. Create a Deis Cluster
2. Deploy an App
3. Destroy the App
4. Check the /home/git/ folder and it shouldn't contain the created app git repo

   Pull Request Hygiene TODOs

Please make sure the below checklist is complete.

• [x] Your pull request is concise and to the point (make another PR for refactoring nearby code)
• [x] Your commits are squashed into logical units of work
• [x] Your commits follow the commit style guidelines

[arschles]

@kmala great catch, and I take full responsibility for making the mistake in the first place (doh!) I've marked LGTM, and checked off the boxes above (under Pull Request Hygiene TODOs - in the future, can you check those off when they're done?)

Thanks!

[arschles]

@kmala I see in #280, @MaxenceAdnot says the following: I noticed that a defunct child process linked to boot was consuming a lot of CPU. I agree that this PR cleans up the wait logic a bit, but does it solve the defunct process issue?

[arschles]

@kmala I added a few comments just now, so removed my LGTM. Sorry for the flip-flopping here.

[kmala]

i don't see any defunct process attached to the boot. If you see the issue description in #280 the boot is the one which clearly is taking most of the CPU.

[arschles]

@kmala ok, fair enough. let's keep an eye out for the defunct child process issue then

[MaxenceAdnot]

I'll try to reproduce the case with the defunct child process on my current cluster and I'll let you know. The root cause of these two issues could be different.

EDIT : @arschles @kmala : Here are the defunct child processes I've seen but, my bad, they cannot consume CPU nor RAM by nature and they are probably a kind of trace from a failed push I think.

root     12342 92.9  0.2  23052 18956 ?        Ssl  Mar30 1921:16  \_ boot server
root     25779  0.0  0.0      0     0 ?        Z    Mar30   0:00      \_ [pre-receive] <defunct>
root     26513  0.0  0.0      0     0 ?        Z    Mar30   0:00      \_ [pre-receive] <defunct>

[kmala]

@MaxenceAdnot Yes...your defunct process are from git push failure