core: log: support overlapping filters

currently we filter using simple substitution, this is not good for
overlapping patterns.

filter:

 aaabbbccc

when filter is:

 bbb
 aaabbbccc

or:

 bcc
 bbb

etc...

Change-Id: I512425cf2d1f56cdaf1c386fa105f7e335ae10c4
Signed-off-by: Alon Bar-Lev <alonbl@redhat.com>