Allow setting temp path for remote build

[jficz]

It's getting quite common lately that builds take up a lot of space in /tmp which is also rather often a tmpfs.

Some of my target machines don't have enough RAM to accommodate for such builds. Previously I just set $TMPDIR to something else before building but that can't be done when building on the remote machine with deploy-rs.

There's --temp-path arg but that's used for something else. Something like --temp-build-path or even using --temp-path for builds, too, would be nice.

[jficz]

Somehow even when I set remoteBuild to false and export TMPDIR=/tmp2, I still end up with out of space errors from /tmp/... when building a machine which happens to be the localhost. Not sure if this is a deploy issue or nix issue. See #283