use relative shlib path

This got lost when cleaning up shlib dependencies. The shlibs should be found relative to the executables to make YARR relocatable. Backported from master

mkdir ~/test_dir
cp -r bin lib ~/test_dir

after fix

ldd bin/scanConsole
	linux-vdso.so.1 =>  (0x00007ffca79b7000)
	libYarr.so => /home/wittgen/test_dir/bin/../lib/libYarr.so (0x00007fa1aac4b000)
	libSpec.so => /home/wittgen/test_dir/bin/../lib/libSpec.so (0x00007fa1aab91000)
	libEmu.so => /home/wittgen/test_dir/bin/../lib/libEmu.so (0x00007fa1aaa86000)
	libFei4.so => /home/wittgen/test_dir/bin/../lib/libFei4.so (0x00007fa1aa957000)
	libRd53a.so => /home/wittgen/test_dir/bin/../lib/libRd53a.so (0x00007fa1aa84c000)
	libStar.so => /home/wittgen/test_dir/bin/../lib/libStar.so (0x00007fa1aa710000)
	libRd53b.so => /home/wittgen/test_dir/bin/../lib/libRd53b.so (0x00007fa1aa494000)
	libScan.so => /home/wittgen/test_dir/bin/../lib/libScan.so (0x00007fa1aa2b2000)
	libUtil.so => /home/wittgen/test_dir/bin/../lib/libUtil.so (0x00007fa1aa1a3000)
	libpthread.so.0 => /lib64/libpthread.so.0 (0x00007fa1a9f5e000)
	libstdc++.so.6 => /lib64/libstdc++.so.6 (0x00007fa1a9c56000)
	libm.so.6 => /lib64/libm.so.6 (0x00007fa1a9954000)
	libgcc_s.so.1 => /lib64/libgcc_s.so.1 (0x00007fa1a973e000)
	libc.so.6 => /lib64/libc.so.6 (0x00007fa1a9370000)
	/lib64/ld-linux-x86-64.so.2 (0x00007fa1aaa58000)

before

ldd bin/scanConsole
	linux-vdso.so.1 =>  (0x00007fffdcb68000)
	libYarr.so => /home/wittgen/atlas/test_build_yarr/build/lib/libYarr.so (0x00007f523f50a000)
	libSpec.so => /home/wittgen/atlas/test_build_yarr/build/lib/libSpec.so (0x00007f523f450000)
	libEmu.so => /home/wittgen/atlas/test_build_yarr/build/lib/libEmu.so (0x00007f523f345000)
	libFei4.so => /home/wittgen/atlas/test_build_yarr/build/lib/libFei4.so (0x00007f523f216000)
	libRd53a.so => /home/wittgen/atlas/test_build_yarr/build/lib/libRd53a.so (0x00007f523f10b000)
	libStar.so => /home/wittgen/atlas/test_build_yarr/build/lib/libStar.so (0x00007f523efcf000)
	libRd53b.so => /home/wittgen/atlas/test_build_yarr/build/lib/libRd53b.so (0x00007f523ed53000)
	libScan.so => /home/wittgen/atlas/test_build_yarr/build/lib/libScan.so (0x00007f523eb71000)
	libUtil.so => /home/wittgen/atlas/test_build_yarr/build/lib/libUtil.so (0x00007f523ea62000)
	libpthread.so.0 => /lib64/libpthread.so.0 (0x00007f523e81d000)
	libstdc++.so.6 => /lib64/libstdc++.so.6 (0x00007f523e515000)
	libm.so.6 => /lib64/libm.so.6 (0x00007f523e213000)
	libgcc_s.so.1 => /lib64/libgcc_s.so.1 (0x00007f523dffd000)
	libc.so.6 => /lib64/libc.so.6 (0x00007f523dc2f000)
	/lib64/ld-linux-x86-64.so.2 (0x00007f523f317000)