Upgrade to ADAM 0.18

[arahuja]

This fixes issues with MdTag parsing in previous versions of ADAM for RNA data.

• Some of the PileupSuite tests had to be updated to account for this
  • One had an incorrect CIGAR string
  • One was testing P operators, which was not supported in ADAM. I removed this test for now, but added in the functionality in ADAM P Operator parsing for MDTag bigdatagenomics/adam#875

[timodonnell]

Thanks for taking care of this long-standing annoyance @arahuja . We should add back the failing test once your ADAM fix goes in (perhaps comment it out here?) LGTM

[arahuja]

@timodonnell I'll open an issue with the relavant commit with the test so we can add it back. I do want to investigate first the usage of CIGAR P. We also have an odd comment on in it in PileupElement https://github.com/hammerlab/guacamole/blob/master/src/main/scala/org/hammerlab/guacamole/pileup/PileupElement.scala#L132-L133