tools: replace usage of deprecated egrep
tools: replace usage of deprecated egrep

Since grep 3.8, there is now a warning about egrep being deprecated and
users should switch to `grep -E`.

martinpitt/cockpit,cockpit-project/cockpit,martinpitt/cockpit,cockpit-project/cockpit,cockpit-project/cockpit,martinpitt/cockpit,martinpitt/cockpit,cockpit-project/cockpit,martinpitt/cockpit,cockpit-project/cockpit