Tweak ApiClientInfoTest::testGetUrlInfo

assertTrue() is evil since whenever it fails it gives meaningless output
such as:

 Failed asserting that false is true.

is_string() can be replaced by the assertInternalType() which will
provide a meaningful output such as:

 $this->assertInternalType('string', 42);
 // Failed asserting that 42 is of type "string".

Change-Id: Ic14eec5c5281c96c53079af3ec22786f912aee18