compress/bzip2: fix benchmark to actually measure decompression rate
compress/bzip2: fix benchmark to actually measure decompression rate

Motivation:
* Previously, the size of the compressed data was used for metrics,
rather than the uncompressed size. This causes the library to appear
to perform poorly relative to C or other implementation. Switch it
to use the uncompressed size so that it matches how decompression
benchmarks are usually done (like in compress/flate). This also makes
it easier to compare bzip2 rates to other algorithms since they measure
performance in this way.
* Also, reset the timer after doing initialization work.

Change-Id: I32112c2ee8e7391e658c9cf31039f70a689d9b9d
Reviewed-on: https://go-review.googlesource.com/17611
Reviewed-by: Brad Fitzpatrick <ae9783c0b0efc69cd85ab025ddd17aa44cdc4aa5@golang.org>
Run-TryBot: Brad Fitzpatrick <ae9783c0b0efc69cd85ab025ddd17aa44cdc4aa5@golang.org>
TryBot-Result: Gobot Gobot <66cb808b70d30c07676d5e946fee83fd561249e5@golang.org>

josharian/go,derekmarcotte/go,polyverse-security/go,theif519/go,miolini/go,goodlang/good,josharian/go,linux-on-ibm-z/go,binarycrusader/go,nawawi/go,polyverse-security/go,binarycrusader/go,vsekhar/elastic-go,goodlang/good,codestation/go,ImJasonH/go,cloudflare/go,miolini/go,josharian/go,nawawi/go,codestation/go,CAFxX/go,binarycrusader/go,suncycheng/go,polyverse-security/go,Samurais/go,vanloswang/go,nawawi/go,akutz/go,Samurais/go,derekmarcotte/go,ganboing/go-esx,derekmarcotte/go,theif519/go,vsekhar/elastic-go,miolini/go,mwhudson/go,ImJasonH/go,mwhudson/go,polyverse-security/go,vsekhar/elastic-go,nawawi/go,Samurais/go,vsekhar/elastic-go,suncycheng/go,golang/go,suncycheng/go,josharian/go,binarycrusader/go,CAFxX/go,josharian/go,ImJasonH/go,suncycheng/go,Cofyc/go,cloudflare/go,ganboing/go-esx,ganboing/go-esx,vanloswang/go,4ad/go,theif519/go,cloudflare/go,CAFxX/go,vanloswang/go,Cofyc/go,miolini/go,cloudflare/go,Samurais/go,4ad/go,christopher-henderson/Go,nawawi/go,binarycrusader/go,4ad/go,CAFxX/go,theif519/go,Samurais/go,golang/go,linux-on-ibm-z/go,4ad/go,golang/go,binarycrusader/go,akutz/go,nawawi/go,Samurais/go,miolini/go,akutz/go,mwhudson/go,momchil-velikov/go,goodlang/good,nawawi/go,CAFxX/go,binarycrusader/go,miolini/go,codestation/go,ganboing/go-esx,ImJasonH/go,vsekhar/elastic-go,Samurais/go,momchil-velikov/go,Cofyc/go,momchil-velikov/go,akutz/go,mwhudson/go,4ad/go,4ad/go,derekmarcotte/go,goodlang/good,nawawi/go,theif519/go,Cofyc/go,linux-on-ibm-z/go,suncycheng/go,vanloswang/go,CAFxX/go,binarycrusader/go,codestation/go,theif519/go,linux-on-ibm-z/go,mwhudson/go,golang/go,goodlang/good,ganboing/go-esx,akutz/go,golang/go,suncycheng/go,suncycheng/go,ImJasonH/go,codestation/go,theif519/go,mwhudson/go,josharian/go,CAFxX/go,Cofyc/go,polyverse-security/go,ganboing/go-esx,momchil-velikov/go,momchil-velikov/go,momchil-velikov/go,polyverse-security/go,cloudflare/go,CAFxX/go,vsekhar/elastic-go,polyverse-security/go,golang/go,ImJasonH/go,mwhudson/go,Cofyc/go,ganboing/go-esx,vsekhar/elastic-go,mwhudson/go,vanloswang/go,vanloswang/go,golang/go,josharian/go,codestation/go,linux-on-ibm-z/go,cloudflare/go,momchil-velikov/go,linux-on-ibm-z/go,4ad/go,linux-on-ibm-z/go,derekmarcotte/go,akutz/go,golang/go,derekmarcotte/go,goodlang/good,vanloswang/go,miolini/go,vsekhar/elastic-go,Cofyc/go,4ad/go,linux-on-ibm-z/go,polyverse-security/go,Samurais/go,momchil-velikov/go,ImJasonH/go,codestation/go,cloudflare/go,derekmarcotte/go,goodlang/good,suncycheng/go,theif519/go,cloudflare/go,Cofyc/go,derekmarcotte/go,akutz/go,josharian/go,vanloswang/go,akutz/go,ganboing/go-esx,codestation/go,goodlang/good,ImJasonH/go,miolini/go