Fix genotype validation error message

[ldgauthier]

Actually report the VC alleles as the VC alleles, not the genotype alleles. Current error message is incorrect and not helpful.

[codecov-commenter]

Codecov Report

Merging #1499 into master will decrease coverage by 0.003%. The diff coverage is 0.000%.

@@               Coverage Diff               @@
##              master     #1499       +/-   ##
===============================================
- Coverage     69.243%   69.240%   -0.003%     
  Complexity      8792      8792               
===============================================
  Files            592       592               
  Lines          34860     34860               
  Branches        5815      5815               
===============================================
- Hits           24138     24137        -1     
- Misses          8420      8421        +1     
  Partials        2302      2302               

Impacted Files	Coverage Δ	Complexity Δ
.../htsjdk/variant/variantcontext/VariantContext.java	78.004% <0.000%> (ø)	237.000 <0.000> (ø)
...samtools/util/AsyncBlockCompressedInputStream.java	72.000% <0.000%> (-4.000%)	12.000% <0.000%> (-1.000%)
...htsjdk/samtools/util/nio/DeleteOnExitPathHook.java	90.476% <0.000%> (+9.524%)	4.000% <0.000%> (+1.000%)