crypto/tls: use io.ReadFull in conn_test.go
crypto/tls: use io.ReadFull in conn_test.go

An io.Reader does not guarantee that it will read in the entire buffer.
To ensure that property, io.ReadFull should be used instead.

Change-Id: I0b863135ab9abc40e813f9dac07bfb2a76199950
Reviewed-on: https://go-review.googlesource.com/37403
Reviewed-by: Mikio Hara <e2f4d2eec1d9a1f781345cdd7260d7d52e6468ae@gmail.com>
Run-TryBot: Mikio Hara <e2f4d2eec1d9a1f781345cdd7260d7d52e6468ae@gmail.com>
TryBot-Result: Gobot Gobot <66cb808b70d30c07676d5e946fee83fd561249e5@golang.org>

akutz/go,vsekhar/elastic-go,Cofyc/go,josharian/go,derekmarcotte/go,nawawi/go,codestation/go,linux-on-ibm-z/go,polyverse-security/go,ImJasonH/go,cloudflare/go,josharian/go,josharian/go,linux-on-ibm-z/go,linux-on-ibm-z/go,cloudflare/go,ImJasonH/go,polyverse-security/go,vsekhar/elastic-go,josharian/go,nawawi/go,ImJasonH/go,ImJasonH/go,derekmarcotte/go,golang/go,codestation/go,ImJasonH/go,Cofyc/go,polyverse-security/go,vsekhar/elastic-go,cloudflare/go,akutz/go,CAFxX/go,derekmarcotte/go,nawawi/go,Cofyc/go,CAFxX/go,christopher-henderson/Go,codestation/go,derekmarcotte/go,Cofyc/go,akutz/go,CAFxX/go,codestation/go,linux-on-ibm-z/go,codestation/go,polyverse-security/go,nawawi/go,Cofyc/go,CAFxX/go,akutz/go,akutz/go,ImJasonH/go,CAFxX/go,vsekhar/elastic-go,derekmarcotte/go,polyverse-security/go,vsekhar/elastic-go,josharian/go,codestation/go,vsekhar/elastic-go,golang/go,linux-on-ibm-z/go,derekmarcotte/go,vsekhar/elastic-go,cloudflare/go,ImJasonH/go,polyverse-security/go,linux-on-ibm-z/go,nawawi/go,akutz/go,cloudflare/go,ImJasonH/go,Cofyc/go,golang/go,akutz/go,josharian/go,linux-on-ibm-z/go,nawawi/go,codestation/go,CAFxX/go,golang/go,vsekhar/elastic-go,josharian/go,golang/go,golang/go,nawawi/go,golang/go,codestation/go,Cofyc/go,nawawi/go,cloudflare/go,akutz/go,CAFxX/go,CAFxX/go,cloudflare/go,josharian/go,derekmarcotte/go,linux-on-ibm-z/go,polyverse-security/go,derekmarcotte/go,golang/go,Cofyc/go,cloudflare/go,polyverse-security/go