Allow for configurable excluded directories.

[djnym]

Sometimes in RPM's you need to exclude directories from the file
lists. Before it was a hardcoded list of 3 directories. This
allows you to specify directories via a new command line option.

[djnym]

Similar to other test, ran on

NAME="openSUSE Leap"
VERSION="42.2"
ID=opensuse
ID_LIKE="suse"
VERSION_ID="42.2"
PRETTY_NAME="openSUSE Leap 42.2"
ANSI_COLOR="0;32"
CPE_NAME="cpe:/o:opensuse:leap:42.2"
BUG_REPORT_URL="https://bugs.opensuse.org"
HOME_URL="https://www.opensuse.org/"

But with some slightly different commands

> mkdir foo && cd foo && mkdir tmp && mkdir -p etc/init.d && echo "stuff" > tmp/foo && echo '#!/bin/sh' > etc/init.d/foo && echo 'echo "hello world"' >> etc/init.d/foo ; mkdir -p usr/bin ; echo '#!/bin/sh' > usr/bin/foo.sh ; echo 'echo hello world' >> usr/bin/foo.sh
> ../epm.erl -f -t rpm -n test -v 1.1.0 -a x86_64 tmp etc usr
> rpm -qlp test-1.1.0-1.x86_64.rpm
/etc/init.d/foo
/tmp/foo
/usr/bin
/usr/bin/foo.sh

Notice /usr/bin is in the list and probably shouldn't be as that's a common shared directory. So with this patch

> mkdir foo && cd foo && mkdir tmp && mkdir -p etc/init.d && echo "stuff" > tmp/foo && echo '#!/bin/sh' > etc/init.d/foo && echo 'echo "hello world"' >> etc/init.d/foo ; mkdir -p usr/bin ; echo '#!/bin/sh' > usr/bin/foo.sh ; echo 'echo hello world' >> usr/bin/foo.sh
> ../epm.erl -f -t rpm -n test -v 1.1.0 -a x86_64 --exclude-dir tmp --exclude-dir usr --exclude-dir usr/bin --exclude-dir etc --exclude-dir etc/init.d tmp etc usr
> > rpm -qlp test-1.1.0-1.x86_64.rpm
/etc/init.d/foo
/tmp/foo
/usr/bin/foo.sh

Common directories have been excluded. The default is to use the hardcoded list you had before, so it should behave the same if you don't include any '--exclude-dir' args.