ares_getaddrinfo(): do not use search domains if ARES_FLAG_NOSEARCH is set

[petrvh]

c-ares init options defines a flag ARES_FLAG_NOSEARCH that is supposed to prevent search using configured domain suffixes.

however when using ares_getaddrinfo() the flag was ignored and domain suffixes were used anyway.

Unfortunately explicitly configuring zero domains to search also does not work (if ndomains == 0 default domain search list is loaded regardless of the flag ARES_OPT_DOMAINS being set).

this change adds a check for the ARES_FLAG_NOSEARCH in as_is_only() function that is used by ares_getaddrinfo() to decide if to try to query next possible name ( next_dns_lookup() )

[bradh352]

At first glance this seems to make sense. My guess is this probably broke in the 1.16 timeframe when getaddrinfo was introduced and gethostbyname was made as a wrapper around getaddrinfo, so I think getaddrinfo has never supported this.

We probably need to add an explicit test case for this.

[petrvh]

I can also see that the condition in function as_is_first()

if (hquery->name != NULL && nname && hquery->name[nname - 1] == '.') {

essentially implements the logic of as_is_only() so it can be replaced by call to this function, it also makes sense as "as_is_only" should imply "as_is_first" (and only)

[petrvh]

#637