build: add a `Prepare ccache` job in Travis

Combined compile and test of Node.js where lots of files need to be
compiled (e.g. after a V8 update) is exceeding the time limit for
Travis jobs (50 minutes).

Add a job to Travis that compiles Node.js but doesnt run any tests to
populate the ccache. Introduce staging and move the `Test Suite` job
into a later stage so that it can use the populated ccache.

PR-URL: https://github.com/nodejs/node/pull/27002


Reviewed-By: Refael Ackermann <refack@gmail.com>
Reviewed-By: Rich Trott <rtrott@gmail.com>
Signed-off-by: Beth Griggs <Bethany.Griggs@uk.ibm.com>