Prepare 1.10.0rc2. (#6702)
Prepare 1.10.0rc2. (#6702)

`1.10.0rc2` was previously partially prepared, but issues were encountered that prevented it from ever being released. Let's try it again.
twitter/pants,wisechengyi/pants,tdyas/pants,benjyw/pants,twitter/pants,pantsbuild/pants,tdyas/pants,twitter/pants,wisechengyi/pants,twitter/pants,jsirois/pants,pantsbuild/pants,tdyas/pants,pantsbuild/pants,wisechengyi/pants,benjyw/pants,wisechengyi/pants,pantsbuild/pants,tdyas/pants,tdyas/pants,benjyw/pants,wisechengyi/pants,benjyw/pants,wisechengyi/pants,wisechengyi/pants,twitter/pants,tdyas/pants,twitter/pants,pantsbuild/pants,jsirois/pants,benjyw/pants,benjyw/pants,tdyas/pants,tdyas/pants,pantsbuild/pants,pantsbuild/pants,wisechengyi/pants,twitter/pants,benjyw/pants,jsirois/pants,twitter/pants,tdyas/pants,twitter/pants,wisechengyi/pants