[Build] Rust / cargo isn't available in ubertool

Our release process and instructions are still using the ubertool docker with every language SDK tool installed, but it doesn't include Rust yet.  While we should probably look into a lighter method (like github actions does), this needs to be fixed for the next release.

Cleaning
+ cd lang/php
+ ./build.sh clean
+ cd lang/perl
+ ./build.sh clean
+ cd lang/rust
+ ./build.sh clean
./build.sh: line 26: cargo: command not found