sparse_dd: simplify logging by using syslog

Signed-off-by: David Scott <dave.scott@eu.citrix.com>
sparse_dd: document the 'experimental-reads-bypass-tapdisk' option in the config file

Signed-off-by: David Scott <dave.scott@eu.citrix.com>
cli: add a 'hybrid' format along with 'vhd' and 'raw'

A 'hybrid' source is expected to take the form 'raw_source:vhd_source'
and the stream will contain copies from 'raw_source' based on BAT
information provided via 'vhd_source'.

Signed-off-by: David Scott <dave.scott@eu.citrix.com>
vhd: Vhd_IO.get_sector_location returns a sector

For consistency this function works entirely in sector offsets.
It simply maps a virtual sector offset to a physical sector offset.

Signed-off-by: David Scott <dave.scott@eu.citrix.com>
cli: when writing to raw with --prezeroed, we need to be able to seek

Signed-off-by: David Scott <dave.scott@eu.citrix.com>
sparse_dd: only read vhd metadata from a tapdisk device if it's using the vhd driver

If the disk is actually raw, then the disk could legitimately contain
data which looks like a vhd header, causing confusion.

Signed-off-by: David Scott <dave.scott@eu.citrix.com>
Merge pull request #5 from djs55/fallback-to-boring-copy

Add 'hybrid' of raw with BAT information