perf script python: Add support for sqlite3 to call-graph-from-sql.py

Add support for SQLite 3 to the call-graph-from-sql.py script. The SQL
statements work as is, so just detect the database type by checking if the
SQLite 3 file exists.

Committer notes:

Tested collecting the PT data on a RHEL7.4, generating the SQLite3
database there and then moving it to a Fedora 26 system where the
call-graph-from-sql.py script was run, using python-pyside version
1.2.2-7fc26 to see the callgraphs using Qt4.
Signed-off-by: Adrian Hunter <adrian.hunter@intel.com>
Tested-by: Arnaldo Carvalho de Melo <acme@redhat.com>
Link: http://lkml.kernel.org/r/1501749090-20357-6-git-send-email-adrian.hunter@intel.comSigned-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>

tools/perf/scripts/python/call-graph-from-sql.py

 #!/usr/bin/python2
-# call-graph-from-sql.py: create call-graph from postgresql database
+# call-graph-from-sql.py: create call-graph from sql database
 # Copyright (c) 2014-2017, Intel Corporation.
 #
 # This program is free software; you can redistribute it and/or modify it
@@ -11,16 +11,17 @@
 # FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License for
 # more details.
 
-# To use this script you will need to have exported data using the
-# export-to-postgresql.py script.  Refer to that script for details.
+# To use this script you will need to have exported data using either the
+# export-to-sqlite.py or the export-to-postgresql.py script.  Refer to those
+# scripts for details.
 #
-# Following on from the example in the export-to-postgresql.py script, a
+# Following on from the example in the export scripts, a
 # call-graph can be displayed for the pt_example database like this:
 #
 #	python tools/perf/scripts/python/call-graph-from-sql.py pt_example
 #
-# Note this script supports connecting to remote databases by setting hostname,
-# port, username, password, and dbname e.g.
+# Note that for PostgreSQL, this script supports connecting to remote databases
+# by setting hostname, port, username, password, and dbname e.g.
 #
 #	python tools/perf/scripts/python/call-graph-from-sql.py "hostname=myhost username=myuser password=mypassword dbname=pt_example"
 #
@@ -296,8 +297,19 @@ if __name__ == '__main__':
 
 	dbname = sys.argv[1]
 
+	is_sqlite3 = False
+	try:
+		f = open(dbname)
+		if f.read(15) == "SQLite format 3":
+			is_sqlite3 = True
+		f.close()
+	except:
+		pass
+
+	if is_sqlite3:
+		db = QSqlDatabase.addDatabase('QSQLITE')
+	else:
 		db = QSqlDatabase.addDatabase('QPSQL')
-
 		opts = dbname.split()
 		for opt in opts:
 			if '=' in opt: