Drop drive letter from path to razor root when RAZOR_ROOT set.

If the RAZOR_ROOT environment variable was set to eg., /root then on
Microsoft Windows we were trying to use paths such as /rootC:/Programs
which is obviously wrong. Instead we should drop the drive letter
giving paths of the form /root/Programs. Note that the drive letter is
_not_ migrated to C:/root/Programs: If a root of C:/root was desired
then RAZOR_ROOT would have been set to C:/root.

 #!/bin/sh

 export RAZOR_ROOT=`mktemp -dt` || exit 1

 ../src/razor init || exit 1

 export YUM_URL="file://localhost/`pwd`"

 ../src/razor import-yum || exit 1

 ../src/razor install zsh2 || exit 1

 ../src/razor info zsh2 > details.out || exit 1

 diff -u $srcdir/details.ref details.out || exit 1

 rm -rf "$RAZOR_ROOT"