containers: add --build option to run.sh
containers: add --build option to run.sh

Add an option to skip running the tests.  This is useful in combination
with 'make unit-tests-container-shell' to prepare and build the tree, in
preparation for manual testing.

Closes #11908
cockpit-project/cockpit,cockpit-project/cockpit,deryni/cockpit,mvollmer/cockpit,martinpitt/cockpit,moraleslazaro/cockpit,moraleslazaro/cockpit,deryni/cockpit,garrett/cockpit,cockpituous/cockpit,cockpituous/cockpit,cockpituous/cockpit,deryni/cockpit,deryni/cockpit,martinpitt/cockpit,cockpit-project/cockpit,mvollmer/cockpit,mvollmer/cockpit,mvollmer/cockpit,moraleslazaro/cockpit,moraleslazaro/cockpit,martinpitt/cockpit,cockpit-project/cockpit,cockpituous/cockpit,moraleslazaro/cockpit,deryni/cockpit,garrett/cockpit,cockpituous/cockpit,deryni/cockpit,cockpituous/cockpit,deryni/cockpit,martinpitt/cockpit,garrett/cockpit,cockpit-project/cockpit,garrett/cockpit,martinpitt/cockpit,garrett/cockpit,mvollmer/cockpit,moraleslazaro/cockpit,moraleslazaro/cockpit