Set application name for API calls

[chanseokoh]

Fixes #41.

[codecov-io]

Codecov Report

Merging #43 into master will increase coverage by 0.28%.

@@            Coverage Diff             @@
##           master      #43      +/-   ##
==========================================
+ Coverage   78.47%   78.76%   +0.28%     
==========================================
  Files          10       10              
  Lines         223      226       +3     
  Branches       20       20              
==========================================
+ Hits          175      178       +3     
  Misses         42       42              
  Partials        6        6

Impacted Files	Coverage Δ
...com/google/cloud/tools/login/GoogleLoginState.java	75.67% <100%> (+0.67%)	:white_check_mark:

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[chanseokoh]

PTAL

[chanseokoh]

PATL @elharo