Fix misinterpretation of maxAttempts

[igorbernstein2]

0 means unlimited attempts not disable retries. Also:

• add some tests to prevent this from happening again
• fix a broken test

[codecov-io]

Codecov Report

Merging #497 into master will increase coverage by 0.23%.
The diff coverage is 75%.

@@             Coverage Diff              @@
##             master     #497      +/-   ##
============================================
+ Coverage      70.5%   70.73%   +0.23%     
- Complexity      810      811       +1     
============================================
  Files           165      165              
  Lines          3774     3773       -1     
  Branches        289      286       -3     
============================================
+ Hits           2661     2669       +8     
+ Misses          990      982       -8     
+ Partials        123      122       -1

Impacted Files	Coverage Δ	Complexity Δ
...a/com/google/api/gax/grpc/GrpcCallableFactory.java	69.81% <100%> (+2.53%)	7 <0> (-1)	⬇️
...rc/main/java/com/google/api/gax/rpc/Callables.java	66.66% <66.66%> (+3.03%)	7 <2> (+1)	⬆️
.../java/com/google/api/gax/grpc/GrpcCallContext.java	80% <0%> (+6.66%)	31% <0%> (+1%)	⬆️

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[garrettjonesgoogle]

@vam-google could you take a look?

[vam-google]

LGTM

[igorbernstein2]

Please merge when ready