tools+stubdom: install under /usr/local by default.

tools+stubdom: install under /usr/local by default.

This is the defacto (or FHS mandated?) standard location for software
built from source, in order to avoid clashing with packaged software
which is installed under /usr/bin etc.

I think there is benefit in having Xen's install behave more like the
majority of other OSS software out there.

The major downside here is in the transition from 4.2 to 4.3 where
people who have built from source will innevitably discover breakage
because 4.3 no longer overwrites stuff in /usr like it used to so they
pickup old stale bits from /usr instead of new stuff from /usr/local.

Packages will use ./configure --prefix=/usr or whatever helper macro
their package manager gives them. I have confirmed that doing this
results in the same list of installed files as before this patch was
applied.

The hypervisor remains in /boot/ and there is no intention to move it.

Signed-off-by: Ian Campbell <ian.campbell@citrix.com>
Acked-by: Roger Pau Monné <roger.pau@citrix.com>
Acked-by: Matt Wilson <msw@amazon.com>
Committed-by: Ian Campbell <ian.campbell@citrix.com>