Improve error message for missing transaction lock

Give the user a hint that running rpm as root will fix the issue.

Resolves: rpm-software-management#3886

Author: ffesti

lib/rpmlock.cc

@@ -124,6 +124,8 @@ rpmlock rpmlockNew(const char *lock_path, const char *descr)
     if (!lock) {
 	rpmlog(RPMLOG_ERR, _("can't create %s lock on %s (%s)\n"), 
 		descr, lock_path, strerror(errno));
+	if (errno == ENOENT && geteuid() != 0)
+	    rpmlog(RPMLOG_ERR, _("\trun rpm with write permission to the rpmdb once to create the lock file\n"));
     }
     return lock;
 }

tests/rpmdb.at

@@ -587,16 +587,21 @@ RPMTEST_SETUP_RW([rpmdb --rebuilddb and verify empty database])
 AT_KEYWORDS([rpmdb])
 RPMTEST_CHECK([
 RPMDB_RESET
+RPMTEST_USER
 runroot rpmdb --rebuilddb
 runroot ls `rpm -E "%{_dbpath}/.rpm.lock"`
 runroot rpmdb --verifydb
 runroot ls `rpm -E "%{_dbpath}/.rpm.lock"`
+runroot rm `rpm -E "%{_dbpath}/.rpm.lock"`
+runroot_user rpm -qa
 ],
 [0],
 [/var/lib/rpm-testsuite/.rpm.lock
 /var/lib/rpm-testsuite/.rpm.lock
 ],
-[])
+[error: can't create transaction lock on /var/lib/rpm-testsuite/.rpm.lock (No such file or directory)
+error: 	run rpm with write permission to the rpmdb once to create the lock file
+])
 RPMTEST_CLEANUP
 
 # ------------------------------