[tar] Improve performance of -c/-x/-t. * Fixes performance of -c and -x by increasing the buffer size from 512 bytes to 8192 bytes. * Fixes performance of -t by using lseek instead of reading the data. * Prevents incorrect error message when trying to remove a directory that contains files. * Filed related bugs US-291, US-293 and US-294. US-295 #done Change-Id: Id971750fa6bd6d45c27bef65b72986eb20d3db70