fedora: Add persistent sudo to bootstrap.sh

Since sudo times out after 5 minutes, and since we don't want to run
every command as root, we can instead create a "persistent sudo" by
invoking the sudo command at least once within 5 minute time frames.

This script does just that, and solves the problem of sudo timing out
after a long command.

.fedora/bootstrap.sh

@@ -6,8 +6,18 @@ set -e
 # Change the working directory to this one
 cd "$(dirname "$0")"
 
+# Get administrative privileges
+sudo -v
+
+# Keep pinging sudo until this script finishes
+# Source: https://gist.github.com/cowboy/3118588
+while true; do sudo -n true; sleep 60; kill -0 "$$" || exit; done 2>/dev/null &
+
 # Install dependencies
-sudo dnf install -y make fedpkg
+sudo -n dnf install -y make fedpkg
 
 # Run make
 make
+
+# Revoke privileges
+sudo -K