redis: move all config modifications to prepare()

Signed-off-by: Gregory Petrosyan <gregory.petrosyan@gmail.com>
redis: make 'install' arguments more uniform

Signed-off-by: Gregory Petrosyan <gregory.petrosyan@gmail.com>
redis: do not override allocator specified in upstream source

Signed-off-by: Gregory Petrosyan <gregory.petrosyan@gmail.com>