encoding/pem: do not try to round trip value with leading/trailing space
encoding/pem: do not try to round trip value with leading/trailing space

The header is literally

	Key: Value

If the value or the key has leading or trailing spaces, those will
be lost by the round trip.

Found because testing/quick returns different values now.

Change-Id: I0f574bdbb5990689509c24309854d8f814b5efa0
Reviewed-on: https://go-review.googlesource.com/39211
Run-TryBot: Russ Cox <5ad239cb8a44f659eaaee0aa1ea5b94947abe557@golang.org>
TryBot-Result: Gobot Gobot <66cb808b70d30c07676d5e946fee83fd561249e5@golang.org>
Reviewed-by: Brad Fitzpatrick <ae9783c0b0efc69cd85ab025ddd17aa44cdc4aa5@golang.org>

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