Reduce number of resume attempts and delay between attempts.

This reduces the number of resume attempts from 20 to 3 (total
4 attempts), and the delay between a failure and the subsequent attempt
from 60 to 20 seconds.  In total, the delay induced due to resume
attempts will not exceed 1 minute.  This appears long enough to overcome
transient connectivity issues such as a user moving between access
points, a temporary Ethernet cable disconnect, or a switch restarting.
It is necessary for reducing the amount of time a user needs to wait in
the case of interrupted network connectivity during OOBE update.

This requires a corresponding fix to unittests, as the assumption on the
number of retries has changed.

BUG=chrome-os-partner:7961
TEST=Passed unittests; verifying OOBE behavior pending at test lab.

Change-Id: I669ac6e2a1264c1d154b23a06c66763f155ab946
Reviewed-on: https://gerrit.chromium.org/gerrit/15639
Reviewed-by: Gilad Arnold <[email protected]>
Tested-by: Gilad Arnold <[email protected]>
Commit-Ready: Gilad Arnold <[email protected]>

http_fetcher_unittest.cc

@@ -30,8 +30,8 @@ namespace {
 
 const int kBigLength           = 100000;
 const int kMediumLength        = 1000;
-const int kFlakyTruncateLength = 9000;
-const int kFlakySleepEvery     = 7;
+const int kFlakyTruncateLength = 29000;
+const int kFlakySleepEvery     = 3;
 const int kFlakySleepSecs      = 10;
 
 }  // namespace

libcurl_http_fetcher.cc

@@ -27,7 +27,7 @@ using std::string;
 namespace chromeos_update_engine {
 
 namespace {
-const int kMaxRetriesCount = 20;
+const int kMaxRetriesCount = 3;
 const int kNoNetworkRetrySeconds = 10;
 const char kCACertificatesPath[] = "/usr/share/chromeos-ca-certificates";
 }  // namespace {}

libcurl_http_fetcher.h

@@ -36,7 +36,7 @@ class LibcurlHttpFetcher : public HttpFetcher {
         download_length_(0),
         resume_offset_(0),
         retry_count_(0),
-        retry_seconds_(60),
+        retry_seconds_(20),
         no_network_retry_count_(0),
         no_network_max_retries_(0),
         idle_seconds_(1),