Improve errExit error messages

Changes:

* Move msg to the end of errExit (right before perror(3p))
* Include the full file path (within the repository)
* Add "()" to function name for clarity

Before:

    Error malloc: main.c:123 main: Cannot allocate memory

After:

    Error src/firejail/main.c:123 main(): malloc: Cannot allocate memory

Note: This clarifies which is the exact file that the error message
comes from, as there are many source files with the same name.  For
example:

    $ git ls-files 'src/*/main.c' | wc -l
    20

1 files changed, 1 insertions, 1 deletions

diff --git a/test/appimage/filename.exp b/test/appimage/filename.exp
index 9d9127fb5..f2b827bb6 100755
--- a/test/appimage/filename.exp
+++ b/test/appimage/filename.exp
@@ -24,7 +24,7 @@ after 100
 send -- "firejail --appimage appimage.sh\r"
 expect {
         timeout {puts "TESTING ERROR 2\n";exit}
-        "Error mounting appimage"
+        -re "Error .*mounting appimage"
 }
 after 100