Is the white fluid that is discharged from one who practices masturbation considered maniyy (seminal fluid), and is his puberty thus considered valid, and is his pilgrimage counted as an Islamic pilgrimage?

What you saw may have been madhiy (pre-seminal fluid), which some scholars consider to be linked to semen, thus making it a sign of puberty. There are other signs of puberty as well. If you have confirmed the presence of one of the signs of puberty and performed Hajj this year, your Hajj is considered Hajj al-Islam.