fd_snapshot_loader can't follow snapshot redirects

[ripatel-fd]

Although fd_snapshot_http can follow redirects, fd_snapshot_loader can't.

fd_snapshot_loader attempts to extract the snapshot hash from the input string.
It should try to parse it from the final redirect's URL instead of the first URL.

NOTICE  05-23 15:54:35.499314 369660 6    replay:0 src/flamenco/snapshot/fd_snapshot.c(115): fd_snapshot_load(http://x.x.x.x:8899/incremental-snapshot.tar.bz2, verify-hash=false, check-hash=false, FD_SNAPSHOT_TYPE_INCREMENTAL)
ERR     05-23 15:54:35.499336 369660 6    replay:0 src/flamenco/snapshot/fd_snapshot.c(136): invalid snapshot hash