Use docker environment to build the actors reproducibly

[ianconsolata]

I didn't have permissions to push to the original branch in https://github.com/filecoin-project/builtin-actors/pull/634, so I made my own fork.

[codecov-commenter]

Codecov Report

Merging #865 (df2b7cf) into master (fdcf50b) will increase coverage by 0.02%. The diff coverage is 100.00%.

:exclamation: Current head df2b7cf differs from pull request most recent head 582587e. Consider uploading reports for the commit 582587e to get more accurate results

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #865      +/-   ##
==========================================
+ Coverage   88.08%   88.10%   +0.02%     
==========================================
  Files          95       95              
  Lines       19619    19628       +9     
==========================================
+ Hits        17281    17294      +13     
+ Misses       2338     2334       -4     

Impacted Files	Coverage Δ
runtime/src/test_utils.rs	83.00% <100.00%> (+0.19%)	:arrow_up:
actors/verifreg/src/lib.rs	92.84% <0.00%> (+0.12%)	:arrow_up:
actors/power/src/lib.rs	83.83% <0.00%> (+0.21%)	:arrow_up:
actors/multisig/src/lib.rs	95.04% <0.00%> (+0.23%)	:arrow_up:
actors/init/src/lib.rs	98.14% <0.00%> (+1.85%)	:arrow_up:

[anorth]

Thanks for moving things into Makefile

[ianconsolata]

Just rebased onto filecoin-project/master to bring this PR up to date with recent changes. I think the upgrade from last week has settled enough we should be good to merge this now?