create-profile.sh: make detection of the default_content module more robust

Do not just grep on "$ENABLED_MODULES" which is a comma-separated list
on which is harder to match for the exact module name.

Use instead the output of pm-list which has one module name for each
line, this way it is easier to match for the exact name of
"default_content" and avoid picking up other modules which may contain
the string "default_content" in their names.