Expose the ttl and install_cache properties on CachingObtainer.
Expose the ttl and install_cache properties on CachingObtainer.

They're "public" anyway, in the sense that they're passed into
__init__(). But this allows the PantsObtainer subclass of CachingObtainer
 to access them in a natural way and use them to initialize the temporary
CachingObtainers it delegates to.

Reviewed at https://rbcommons.com/s/twitter/r/267/

Signed-off-by: John Sirois <82d8b9acb65478c2cf98f3a8c11b3322c3423201@twitter.com>

atollena/commons,cevaris/commons,VaybhavSharma/commons,pombredanne/commons,brutkin/commons,WCCCEDU/twitter-commons,Yasumoto/commons,Yasumoto/commons,VaybhavSharma/commons,pombredanne/commons,nkhuyu/commons,abel-von/commons,VaybhavSharma/commons,WCCCEDU/twitter-commons,abel-von/commons,pombredanne/commons,jsirois/commons,nkhuyu/commons,cevaris/commons,pombredanne/commons,brutkin/commons,ericzundel/commons,jsirois/commons,ericzundel/commons,atollena/commons,Yasumoto/commons,abel-von/commons,nkhuyu/commons,ericzundel/commons,atollena/commons,WCCCEDU/twitter-commons,WCCCEDU/twitter-commons,ericzundel/commons,ericzundel/commons,pombredanne/commons,jsirois/commons,abel-von/commons,Yasumoto/commons,WCCCEDU/twitter-commons,nkhuyu/commons,brutkin/commons,cevaris/commons,jsirois/commons,cevaris/commons,cevaris/commons,brutkin/commons,nkhuyu/commons,Yasumoto/commons,brutkin/commons,VaybhavSharma/commons,jsirois/commons,atollena/commons,VaybhavSharma/commons,atollena/commons,abel-von/commons