allocator: improve logs consistency

[thaJeztah]

built on top of https://github.com/docker/swarmkit/pull/2823; only the last commit is new, but thought to keep it separate

[codecov[bot]]

Codecov Report

Merging #2824 into master will decrease coverage by 0.03%. The diff coverage is 52.63%.

@@            Coverage Diff             @@
##           master    #2824      +/-   ##
==========================================
- Coverage   61.62%   61.59%   -0.04%     
==========================================
  Files         139      139              
  Lines       22615    22615              
==========================================
- Hits        13936    13929       -7     
- Misses       7194     7210      +16     
+ Partials     1485     1476       -9

[codecov-commenter]

Codecov Report

Merging #2824 (20c609d) into master (b98a45d) will increase coverage by 0.03%. The diff coverage is 72.72%.

@@            Coverage Diff             @@
##           master    #2824      +/-   ##
==========================================
+ Coverage   61.75%   61.78%   +0.03%     
==========================================
  Files         155      155              
  Lines       31145    31137       -8     
==========================================
+ Hits        19234    19239       +5     
+ Misses      10361    10346      -15     
- Partials     1550     1552       +2