Merge pull request #52660 from kad/npapi

Automatic merge from submit-queue (batch tested with PRs 50988, 50509, 52660, 52663, 52250). If you want to cherry-pick this change to another branch, please follow the instructions <a href="https://github.com/kubernetes/community/blob/master/contributors/devel/cherry-picks.md">here</a>.

To be consistent with http package, check also no_proxy

**What this PR does / why we need it**:
Default http.ProxyFromEnvironment uses uppper case proxy
environment variables first, and if they are not defined,
tries lower case. For NewProxierWithNoProxyCIDR we should
provide similar user experience.
Example: cluster will not be able to access service or pod CIDRs in case user uses lower case version of proxy variables.

**Which issue this PR fixes** *(optional, in `fixes #<issue number>(, fixes #<issue_number>, ...)` format, will close that issue when PR gets merged)*: fixes #

**Special notes for your reviewer**:

**Release note**:
```release-note
NONE
```

staging/src/k8s.io/apimachinery/pkg/util/net/http.go

@@ -256,8 +256,11 @@ func isDefault(transportProxier func(*http.Request) (*url.URL, error)) bool {
 // NewProxierWithNoProxyCIDR constructs a Proxier function that respects CIDRs in NO_PROXY and delegates if
 // no matching CIDRs are found
 func NewProxierWithNoProxyCIDR(delegate func(req *http.Request) (*url.URL, error)) func(req *http.Request) (*url.URL, error) {
-	// we wrap the default method, so we only need to perform our check if the NO_PROXY envvar has a CIDR in it
+	// we wrap the default method, so we only need to perform our check if the NO_PROXY (or no_proxy) envvar has a CIDR in it
 	noProxyEnv := os.Getenv("NO_PROXY")
+	if noProxyEnv == "" {
+		noProxyEnv = os.Getenv("no_proxy")
+	}
 	noProxyRules := strings.Split(noProxyEnv, ",")
 
 	cidrs := []*net.IPNet{}