perf scripts python: exported-sql-viewer.py: Select find text when find bar is activated

The user probably wants to replace the find text, so select the find
text when the find bar is activated.

That is fairly standard behaviour for search text entry.

Entering text will replace the current text, but using edit keys
(arrows, home, end etc) cancels the selection and enables editing.
Signed-off-by: NAdrian Hunter <adrian.hunter@intel.com>
Tested-by: NArnaldo Carvalho de Melo <acme@redhat.com>
Cc: Jiri Olsa <jolsa@redhat.com>
Link: http://lkml.kernel.org/r/20190520113728.14389-23-adrian.hunter@intel.comSigned-off-by: NArnaldo Carvalho de Melo <acme@redhat.com>

tools/perf/scripts/python/exported-sql-viewer.py

@@ -400,6 +400,7 @@ class FindBar():
 
 	def Activate(self):
 		self.bar.show()
+		self.textbox.lineEdit().selectAll()
 		self.textbox.setFocus()
 
 	def Deactivate(self):