tests: Make write file a public torture function.

Signed-off-by: Andreas Schneider <asn@cryptomilk.org>
Reviewed-by: Aris Adamantiadis <aris@0xbadc0de.be>

tests/torture.h

@@ -68,6 +68,8 @@ ssh_session torture_ssh_session(const char *host,
 struct torture_sftp *torture_sftp_session(ssh_session session);
 void torture_sftp_close(struct torture_sftp *t);
 
+void torture_write_file(const char *filename, const char *data);
+
 /*
  * This function must be defined in every unit test file.
  */