Tell user the reason for a failure

Exclamation marks in error messages are most useful if you add a dollar
sign before them!

Also avoid things like "can't" and "don't" in error messages.

lib/OpenQA/Schema.pm

@@ -59,8 +59,8 @@ sub deploy ($self, $force_overwrite = 0) {
     my $dblock;
 
     # LOCK_EX works most reliably if the file is open with write intent
-    open($dblock, '>>', $dblockfile) or die "Can't open database lock file ${dblockfile}!";
-    flock($dblock, LOCK_EX) or die "Can't lock database lock file ${dblockfile}!";
+    open($dblock, '>>', $dblockfile) or die "Cannot open database lock file ${dblockfile}: $!";
+    flock($dblock, LOCK_EX) or die "Cannot lock database lock file ${dblockfile}: $!";
     my $dir = $FindBin::Bin;
     while (abs_path($dir) ne '/') {
         last if (-d "$dir/dbicdh");